6.8 Scoring Rules

6.8.1 Scoring Sleep Stages and Arousals

Scoring will be based on American Academy of Sleep Medicine “The AASM Manual for the Scoring of Sleep and Associated Events Rules, Terminology and Technical Specifications” 2007.

6.8.1.1 Rules for assigning epoch-specific sleep score

Epoch-by-epoch approach: The polygraph record is divided into consecutive segments of equal size (30 s., each termed an “epoch”). Each epoch has assigned a single sleep stage score. The epoch duration is maintained for the duration of the recording.

• When more than one stage is present in an epoch, that epoch is assigned a single stage score reflecting the stage that occupied the greatest portion of the epoch.
• When two stages of sleep are evenly distributed on the epoch, and one of these stages was the same stage as in the preceding epoch, then that epoch will be assigned the same sleep stage as the preceding epoch (*).
• Portions of two epochs may not be combined to create a new epoch.
• When an arousal of <15 sec. occurs within an epoch, the time “in arousal” is not counted when determining the predominant sleep stage time in that epoch.

Terminology for stages of sleep:

• Stage W (Wakefulness)
• Stage N1 (NREM 1)
• Stage N2 (NREM 2)
• Stage N3 (NREM 3) – Represents slow wave sleep and replaced R&K nomenclature of stage 3 and 4
• Stage R (REM)

6.8.1.2 Sleep onset

Sleep onset is defined the start of the first epoch scored as any stage other than stage W.

6.8.1.3 EEG arousal

Scoring arousals is based on “A Preliminary Report from the Sleep Disorders Atlas Task Force of the American Sleep Disorders Association” Sleep, vol. 15, no 2, 1992. (ASDA criteria)

The scoring of EEG arousals is independent from the scoring of sleep stages (i.e. an arousal can be scored in an epoch of recording which would be classified as wake by R & K criteria). An arousal can proceed to the wake stage (by R & K criteria) or can be followed by a return to sleep.

Definition of Arousal:

An EEG arousal is an abrupt shift of EEG frequency including alpha, theta and/or frequencies greater than 16 Hz (but not spindles) lasting at least 3 s., and starting after at least 10 continuous seconds of sleep.

Artifacts, K complexes and delta waves are included in meeting the 3 s. duration criteria only when they occur within the EEG frequency shift (change in frequency must be visible before these waveforms). A "K" complex or spindle occurring immediately prior to the EEG shift or following is not included in the arousal duration.

Parts of the EEG totally obscured by EMG artifact are considered an arousal if the change in background EEG in addition to the area obscured by EMG is at least > 3 sec.

Alpha activity of less than 3 s. duration in Non-REM sleep at a rate greater than one burst per 10 s. is not scored as an EEG arousal. Three seconds of alpha sleep is not scored as an arousal unless a 10 s. episode of alpha free sleep precedes this.

If equivalent EEGs pairs are interpretable, the arousal (EEG frequency shift) must be observed in both channels. If observed in only one of two equivalent channels, the change in EEG is assumed to be artifact and not an arousal. CHAT used more EEG than just the 2 centrals: Frontals [F3/4], Centrals [C3/4], Temporal [T3/4] and Occipitals [O1/2], required to see arousal on both sides of the head.

Arousals lasting > 15 s. and containing awake EEG within an epoch cause the epoch to be classified as AWAKE.

TIPS for Arousals Generally:(*)

• When unsure if change in background EEG represents an abrupt change, look at a 60 sec window and note if there is a discrete change from background EEG.
• Note whether changes were evident on both EEG channels.
• Be careful to distinguish an increase in EEG frequency from EMG artifact (esp. in delta sleep).
• Isolated bursts of delta activity or sawtooth-like waves do not constitute an arousal. In contrast, slow waves intermixed with fast activity that differs from background do qualify as arousals.
• Occasionally, EEG acceleration is superimposed on slower waves. The slowing may be an artifact secondary to movement or burst of delta waves. If there is evidence of embedded EEG acceleration for ≥ 3 sec., mark as an arousal.

Arousal Length - Wake versus Sleep:(*)

Some studies with high RDIs have many arousals that may appear to last > 15 sec. within given epochs. If all such epochs were classified as AWAKE, then the respiratory events would not be included in the RDI and the

RDI will be underestimated. When faced with this situation, and when <1 second duration would change the epoch from sleep to wake, the scorer may attempt to keep the duration of the arousal to as short as feasible to maintain the epoch as sleep (e.g., corresponding to the length of the waking EEG in that epoch.). This will maximize the number of epochs containing arousals that are captured as "sleep".

6.8.1.4 Arousals in REM

In stage REM, an EEG frequency shift must be accompanied by a simultaneous increase in amplitude of the chin EMG (lasting at least 1 second). An arousal starts when a definite change in background EEG is visualized. The increase in the chin EMG can occur anytime during the arousal (can be at the end) and is not a marker for the beginning of the arousal however, increased EMG activity without a change in background EEG does not constitute an arousal.

TIPS for Arousals in REM:(*)

• If the level of REM EMG appears to be fluctuating, then the increase in EMG in the area of a putative arousal needs to be more than the background level of fluctuations, to identify this as a REM arousal.
• A long period of alpha activity before an EMG increase may mark the beginning of the arousal if the alpha activity represents the change in the background pattern.

6.8.1.5 Rules for assigning sleep stages when arousal is present in the epoch

The following rules were established to maximize the amount of sleep identified and thus the number of respiratory events recorded (*):

Brief arousals (e.g. arousals ≤ 15s. long) may require a change in sleep stage. The epoch is staged according to the sleep stage in the remaining parts of the epoch (not including the arousal). After an arousal change to stage N1 until a K complex unassociated with an arousal or a sleep spindle occurs.

The AASM 2007 scoring rules related to major body movement were not used for CHAT. A major body movement would have been scored as an arousal. If the arousal was longer that half the epoch [>15sec of the 30sec epoch] then the epoch was scored wake. Just for reference, the AASM 2007 rules for Major Body Movement are: Definition of Major body movement: movement and muscle artifact obscuring the EEG for more than half an epoch to the extent that the sleep stage cannot be determined.

Rules: Score an epoch with major body movement as follows:

• If alpha rhythm is present for part of the epoch (even <15 seconds duration), score as stage W.
• If no alpha rhythm is discernable, but an epoch scorable as stage W either precedes or follows the epoch with the major body movement, score as stage W.
• Otherwise, score the epoch as the same stage as the epoch that follows it.

Rules for end of stage N2 and end of REM included rule with major body movement.

Rule for end of stage N2: A major body movement followed by slow eye movements and low amplitude mixed frequency EEG without non-arousal associated K complexes or sleep spindles (score the epoch following the major body movement as stage N1; score the epoch as stage N2 if there are no slow eye movements: the epoch containing the body movement is scored using the criteria for major body movement).

Rules for end of REM: A major body movement followed by slow eye movements and low amplitude mixed frequency EEG without non-arousal associated K complexes or sleep spindles (score the epoch following the major body movement as stage N1; if no slow eye movements and the EMG tone remains low, continue to score stage R; the epoch containing the body movement is scored using the criteria for major body movement).

If an arousal or an area of increased EMG causing artifact in the EEG channels is followed by Stage wake (W), then the arousal is considered part of the record scored as a stage Wake. If this part is > 15 s. long, then epoch is scored as a Stage Wake.

In Deep Sleep (unequivocal Stage 3/4), when fast frequency waves are visualized as “riding” on the top of the delta waves, and there are no frequencies characteristic of Stage Wake (*):

• If there is any reason to suspect that the fast frequencies are result of artifact (like a sudden increase in EMG bleeding into EEG), an arousal is not scored.
• When the fast frequencies are not the result of artifact, an arousal is scored. Deep Sleep is scored when delta waves persist despite the faster frequencies riding on top, independent of the length of the arousal.

Note for Delta Sleep (N3): When an arousal includes bursts of Delta waves: these waves are not used for meeting Deep Sleep criteria (e.g. Deep Sleep is scored only if there is ≥ 20 % of the epoch covered by delta waves outside of the arousal).

6.8.1.6 Episodic events in sleep

Sleep spindles: clearly visible, rhythmic bursts of activity 11-16Hz [most commonly12-14 Hz], duration at least 0.5 s. (one should be able to count 5.5 to 8 [most commonly 6 or 7] distinctive waves within a half-second period); the amplitude variability appears sinusoidal.

Sleep spindle activity occurs in adults with a frequency of about three to eight bursts per minute in Stage N2 sleep. These are absent in wakefulness and Stage N1. Spindles may be rarely observed in Stage R and N3. Spindle rate appears to be a fairly stable individual characteristic. In the elderly and in individuals with various medical conditions, sleep spindles tend to lose their classic morphology and may have a slightly slower frequency, lower amplitude, and shorter duration.

Medication effects can introduce beta range activity that may be confused with spindles. Tips to alert to the presence of drug effects mimicking spindles are two or more of the following:

• Increased beta activity (spindle like) in well defined REM sleep and wakefulness.
• Increased spindle duration (often > 1 sec.)
• Increased frequency of spindles per epoch (>5/epoch).
• Spindle like activity with amplitude variability that is NOT sinusoidal.
• Fast frequencies (often > 13 Hz).
• When identifying atypical “spindle activity,” review previous epochs to ascertain if stage was properly scored.
• When atypical spindle like activity is observed, then such activity cannot be used to distinguish Stage N2 from other sleep stages. This may lead to some underscoring of Stage N2 from N1.

K-complex: EEG waveforms having a well-outlined negative sharp wave, immediately followed by a positive component. Total duration of the K complex should exceed 0.5 s. Waves of 12-14 Hz (sleep spindles) may or may not constitute part of K complex. K complexes can occur as a response to sudden auditory stimuli. K complexes may be reflected on the EOG channels. When in doubt about whether a particular polyphasic wave is a “true” K complex, record is scanned for clear Stage N2 sleep. Questionable K complexes are only designated as K complexes if their morphology closely matches those seen in unequivocal Stage N2 sleep. For an arousal to be associated with a K complex, it must commence no more than 1 second after the termination of the K complex.

Hypersynchrony: Bursts of high voltage delta (< 4 Hz) or theta (4 - 7 Hz) waves lasting 2-3 s. with a comb- like morphology with a positive polarity (points up going). Hypersynchrony is not considered an arousal. May need to be distinguished from seizure discharges. In children, this actually may be exaggerated. It is relatively more common during the transition from wakefulness to sleep.

Seizures: This is manifest by an abrupt change in background EEG. This usually requires a wider sampling of areas of the brain than is provided with our montage. Two patterns are commonly seen: 1) High voltage, rhythmic activity in the 2-6 Hz range, or 2) Diffuse sustained beta activity. A seizure is often accompanied by prominent muscle artifact. A seizure is usually followed by low to moderate voltage irregular slowing. On the 10 s. screen, characteristic ‘spikes and wave’ pattern may be seen. If a possible seizure is identified, a physician investigator will be immediately asked to review the study.

6.8.1.7 Rules for assigning sleep stages

EEG frequencies are divided into following bandwidths:

           β  (beta)     > 13 Hz
13 Hz    ≥ α  (alpha)    ≥  8 Hz
 8 Hz    > θ  (theta)    ≥  4 Hz
 4 Hz    > δ  (delta)

An alpha wave is any wave that has the frequency in alpha range. Alpha rhythm (also known as posterior background rhythm, trains of sinusoidal 8-13 Hz activity) has the following characteristics:

• 1) Is seen in the relaxed waking state with the eyes closed.
• 2) Attenuates with eye opening, anxiety or mental activity such as mental calculations
• 3) Slows in drowsiness (occasionally <8 Hz) and then disappears in sleep. The slowing may be so brief as to be unnoticed.
• 4) Generated by occipital lobes and has a broad reflection to temporal and mastoid areas.

Stage W - Waking State

Stage W, when eyes are open, is defined by low voltage, mixed frequency EEG in the alpha and beta ranges (> 8 Hz). When eyes are closed, wake is defined by the presence of the alpha rhythm. There is usually (but not necessarily), a relatively high tonic EMG. Waking shows frequent eye movements and eye blinks. Some subjects may have virtually continuous alpha activity; others may show little or no alpha activity in the waking record. Scoring will be done primarily from C4-M1, F4-M1, and O2-M1 with backup electrodes C3-M2, F3- M2 and O1-M2. Occipital leads will be used for alpha rhythm detection for transitions from wake to sleep.

Rules

• A. Score epochs as stage W when more than 50% of the epoch has alpha rhythm over the occipital region.
• B. Score epochs without visually discernable alpha rhythm as stage W if any of the following are present:
  • 1) Eye blinks at a frequency of 0.5-2 Hz
  • 2) Reading eye movements
  • 3) Irregular conjugate rapid eye movements associated with normal or high chin muscle tone.

Stage 1 sleep [N1]

Stage N1 sleep occurs most often in transition from wakefulness to other sleep stages. Stage N1 is defined by a background of relatively low voltage, mixed frequency EEG activity with noticeable activity in the 4-7 Hz range with no clearly defined non-arousal associated K complexes or sleep spindles in the first half of the epoch. Faster frequencies are mostly lower voltage (amplitude). High voltage (50-75 μV) 4-7 Hz activity tends to occur in irregularly spaced bursts mostly during the later portions of the stage. There are slow eye movements, each of several seconds duration, usually most prominent during early portions of the stage. No rapid eye movements or blinks are present. During the latter portion of the stage, vertex sharp waves, occasionally as high as 200 μV, are often seen in conjunction with high amplitude 4-7 Hz activity. The amount of alpha activity combined with low voltage activity comprises less than half of the epoch. Finally, the tonic EMG level may be lower than observed during relaxed wakefulness.

Traces of low voltage activity at 12-14 Hz may begin to appear as the transition to Stage N2 approaches, but this activity is not defined as a sleep spindles until the rhythmic bursts are clearly visible for at least 0.5 s.

Rules

• A. In subjects who generate alpha rhythm, score stage N1 if alpha rhythm is attenuated and replaced by low amplitude, mixed frequency activity for more than 50% of the epoch.
• B. In subjects who do not generate alpha rhythm, score stage N1 commencing with the earliest of any of the following phenomena:
  • i. Activity in range of 4-7 Hz with slowing of background frequencies by >=1 Hz from those of stage W
  • ii. Vertex sharp waves
  • iii. Slow eye movements

Stage 2 sleep [N2]

Stage N2 is defined by a background similar to Stage N1 sleep with the presence of the non-arousal associated K complexes and/or sleep spindles. It is impossible to define the difference between Stage N1 and Stage N2 sleep on the basis of background activity alone. Bursts of other polymorphic high voltage slow waves, which do not have the precise morphology of K complex, are also frequently seen. Delta waves: high amplitude ( > 75 μV), slow 0.5-2HZ; duration 0.5-2 seconds) activity occupy no more than 19% of the epoch. At the beginning of the Stage N2, slow eye movements may infrequently, and only briefly, persist after the appearance of sleep spindles and non-arousal associated K complexes.

K complexes associated with or imbedded within an arousal do not constitute evidence of Stage N2.

Rules

• A. The following rule defines the start of a period of stage N2 sleep:

  • 1) Begin scoring stage N2 (in absence of criteria for N3) if one or both of the following occur during the first half of that epoch or the last half of the previous epoch:
    • a. One or more K complexes unassociated with arousals
    • b. One or more trains of sleep spindles
  • Note: Continue to score stage N1 for epochs with arousal-associated K complexes but no spontaneous K complexes or sleep spindles.

• B. The following rule defines continuation of a period of stage N2 sleep:

  • 1) Continue to score epochs with low amplitude, mixed frequency EEG activity without K complexes or sleep spindles as stage N2 if they are preceded by a) K complexes unassociated with arousals or b) sleep spindles.

• C. The following rule defines the end of a period of stage N2 sleep:

  • 1) End stage N2 sleep when one of the following events occurs:
    • a) Transition to stage W
    • b) An arousal (change to stage N1 until a K complex unassociated with an arousal or asleep spindle occurs)
    • c) Transition to stage N3
    • d) Transition to stage R

Deep Sleep (N3)

No attempt is made to distinguish Stage 3 from Stage 4 which are combined into a single category: Deep Sleep [N3].

Deep Sleep is scored when 20% or more of the epoch consists of delta waves which are 0.5 Hz-2 Hz and have an amplitude greater than 75 μV [irrespective of age]. The 20% criteria refers specifically to the time occupied by the high amplitude, slow waves, and does not include intervening waves of higher frequency and lower amplitude or K complexes. To fulfill the criteria for Deep Sleep, one should be able to find at least 5-6 high voltage delta waves in the 30second sleep epoch. Delta waves embedded in increased frequency activity (an arousal) do not contribute to the calculation of time in delta sleep.

Sleep spindles and non-arousal associated K complexes may or may not be present in Deep Sleep. Eye movements do not occur in Deep Sleep, although the EOG may reflect the high voltage slow wave activity. The EMG is tonically active, although the tracing may achieve very low levels, indistinguishable from that of REM sleep.

An attempt should be made to distinguish between spontaneous K complexes and delta waves, although this distinction is not always easy. When a K complex distinction is in doubt, comparison should be done with the K complex in unambiguous Stage N2.

Stage REM sleep [R]

Stage R is defined by a background of relatively low voltage, mixed frequency EEG with accompanying episodes of REMs (Rapid Eye Movements). The EEG pattern resembles Stage N1, except that vertex sharp waves are not readily noticeable. Bursts of characteristic “sawtooth” waves may appear, appearing as notched waves in the theta range. Alpha activity is usually more prominent than in Stage N1 and its frequency is 1-2 Hz slower than the alpha rhythm in wakefulness. The EMG reaches its lowest levels (it cannot be higher than the level during the preceding stage). Phasic twitches and intermittent increases of EMG activity may be observed but intervening baseline must remain low. Phasic twitch (EMG) defined as: short (no longer than .10 sec) burst of EMG activity superimposed on suppressed muscle tone which physically manifests as a twitch (contraction) of a muscle or jerk of a limb. In Stage R such muscle contractions may be isolated or become repetitive, but they remain distinctive. Periods of the relatively low voltage, mixed frequency EEG and EMG at Stage R level but without eye movements may follow unambiguous Stage R and is considered Stage R unless criteria for a state change are met.

The EOG shows bursts of rapid eye movements; often the density of such bursts increase as sleep progresses. Thus, earlier Stage R episodes usually contain fewer REMs than later episodes.

Rarely delta waves may be observed in an epoch that is within a period of REM. If occurring within period of REM, a low EMG, continue to score as REM. Large sawtooth waves also may be confused with hypersyncrony.

Start of the Stage REM:

At the start of Stage R, non-arousal associated K complexes, sleep spindles and delta waves end, characteristic sawtooth waves can appear. EMG levels tend to be the lowest after eye movements begin. The fall in EMG may not coincide with the EEG changes.

• If the EMG drops before the last sleep spindle, non-arousal associated K complex or delta wave: Score Stage R from the point the last sleep spindle, non-arousal associated K complex or delta wave was seen.
• Otherwise: Score Stage R from the point where EMG drops. The period of the record before the EMG drop is scored according to the rules for NREM sleep.

Periods of elevated sustained EMG during Stage R sleep:

When EMG is elevated above the REM level, then this portion of the epoch is counted as a Non-REM sleep or WAKE. If phasic twitches or sawtooth waves are seen, but intervening EMG is low, the epoch remains Stage R.

Rules

• A. Score stage R sleep in epochs with all the following phenomena:

  • a. Low amplitude, mixed frequency EEG
  • b. Low chin EMG tone
  • c. Rapid eye movements
  • d. Sawtooth waves [may be helpful when stage is in doubt, but not required for stage R]

• B. The following rule defines the continuation of a period of stage R sleep:

  • Continue to score stage R sleep, even in the absence of rapid eye movements, for epochs following one or more epochs of stage R as defined in A above, if the EEG continues to show low amplitude, mixed frequency activity without non-arousal associated K complexes or sleep spindles and the chin EMG time remains low.

• C. The following rule defines the end of a period of stage R sleep:

  • 1) Stop scoring R sleep when one or more of the following occur:
    • a. There is a transition to stage W, N2, or N3
    • b. An increase in chin EMG tone above the level of R is seen and criteria for stage N1 are met
    • c. An arousal occurs followed by low amplitude, mixed frequency EEG and slow eye movements (score as stage N1; if no slow eye movements and chin EMG tone remains low, continue to score as stage R)
    • d. One or more non-arousal associated K complexes or sleep spindles are present in the first half of the epoch in the absence of rapid eye movements, even if chin EMG tone remains low (score as stage N2). This was modified for CHAT stage dependant on what is seen on following epochs.

• D. Score epochs at the transition between stage N2 and stage R as follows:

  • 1) In between epochs of definite stage N2 and definite stage R, score an epoch with a distinct drop in chin EMG in the first half of the epoch to the level seen in stage R as stage R if all of the following are met, even in the absence of rapid eye movements:
    • a. Absence of non-arousal associated K complexes
    • b. Absence of sleep spindles
  • 2) In between epochs of definite stage N2 and definite stage R, score an epoch with distinct drop in chin EMG in the first half of the epoch to the level seen in stage R as stage N2 if all of the following criteria are met:
    • a. Presence of non-arousal associated K complexes or sleep spindles
    • b. Absence of rapid eye movements
  • 3) In between epochs of definite stage N2 with minimal chin EMG tone and definite stage R without further drop in chin EMG tone, score epochs as stage R if all of the following are met, even in the absence of rapid eye movements:
    • a. Absence of non-arousal associated K complexes
    • b. Absence of sleep spindles

Scoring REM when there are problems with REM related atonia or the EMG is difficult to interpret.

Identification of Stage REM may be difficult when there are prolonged bursts of elevated EMG seen during eye movements or the EMG increases with snoring. In such cases:

• EMG increases clearly related to snoring (changing with breathing) may be ignored, as long as intervening EMG is low.

• The portion of the record with unquestionable Stage R should be reviewed to provide a visual reference of the characteristic Stage R EEG pattern. Stage R is scored when EEG pattern changes to the pattern characteristic for Stage R regardless of the level of the EMG. When EEG is consistent with Stage R, and there is no evidence of wake (blinking), no evidence of Stage N1 (vertex waves, slow rolling eye movements), or the presence of REMs, then score stage Stage R from the last non- arousal associated K complex, sleep spindles or delta wave. Distinguishing between Stage N1 and Stage R is unreliable and noted as such on the PSG scoring notes form.